The subject matter described herein generally relates to a radiation generator and more particularly to a high voltage tank assembly used in a radiation generator.
An imaging system typically comprises a radiation generator and a radiation detector. Generally, the radiation generators are bulky and possess a heavy weight. In some imaging systems, the radiation generator may be balanced with counter weights at the radiation detector to maintain the center of gravity. Alternatively, the radiation generator may be configured to rotate around an object at a speed of several revolutions per second. Therefore, it is desirable to realize a compact radiation generator, in order to avoid adding counterweights and to increase the speed of rotation of the radiation generator. The radiation generator generally comprises a radiation source, a high voltage tank assembly configured to energize the radiation source and a power circuit. As the high voltage tank assembly is responsible for generating the high voltage required for operation of the radiation source and represents a substantial part of the overall size of the radiation generator, it is desirable to provide a compact high voltage tank assembly.
The high voltage tank assembly generally houses a voltage multiplier assembly and a transformer assembly. The voltage potential needed to generate radiation within the radiation source is provided with the help of the voltage multiplier assembly. An alternating current (AC) voltage from the power circuit is fed to the voltage multiplier assembly as an input. The voltage multiplier assembly generally comprises multiple multiplier stages configured to rectify and multiply the applied AC voltage depending on the number of the multiplier stages present.
Each multiplier stage comprises multiple diodes and multiple capacitors. It is desirable to use less number of diodes and capacitors used to form the multiplier stage. Each diode is characterized by a peak inverse voltage (PIV) value. The number of components used in each multiplier stage and the number of multiplier stages used to generate the required high voltage is dependent on the PIV of each diode used in the multiplier stage. A diode with a high value of PIV reduces the number of components and the number of stages required to obtain the desired high voltage. Typically, each multiplier stage uses diodes of PIV value in order of tens of kV. However, using such diodes may not be the cost effective design.
Another known method of manufacturing the voltage multiplier assembly uses diodes with a PIV rating of 1 kV. Multiple diodes with the PIV rating of 1 kV can be connected in series to effectively produce the require PIV for the multiplier stage. The number of diodes used in the voltage multiplier assembly increases multiple folds with the substitution. A drawback of using the diodes with a PIV rating of 1 kV is the difficulty in packing a large number of diodes in a limited space to provide a high voltage supply for the radiation source.
Another drawback of using diodes connected in series is, an existence of unequal distribution of voltage across each diode during transient conditions such as a single shot power turn ON and a high voltage arcing. The voltage distribution under transient conditions is generally influenced by stray capacitances in the voltage multiplier assembly and can lead to unequal distribution of the voltage across the diode arranged in series and thereby results in violation of the PIV rating of the diode.
Generally, the high voltage generated in the radiation source is usually measured with a high voltage component such as, a high voltage resistor divider. The high voltage resistor divider usually has a substantially long structure to ensure sufficient insulation on the surface. The high voltage resistor divider typically comprises a long structure with a high electrical potential at one end and a near ground electrical potential at the other end, thereby creating a non-uniform electric field distribution along the length of the high voltage resistor divider. The non-uniform distribution of electrical potential along the length of the high voltage resistor divider affects the divider ratio during transient conditions and thereby the response and accuracy of measurement.
Further, multiple shields at definite electrical potentials are provided around the high voltage resistor divider to regulate the stray capacitance. The length of the high voltage resistor divider and the shields provided around the high voltage resistor divider make the high voltage resistor divider bulky and voluminous.
Hence, there exists a need to provide a compact and efficient design for assembling various components of a high voltage tank assembly used in the radiation generator.